Control circuit



N m AM A A AVA y I H; H. WITTENBERG 2,445,549 CONTROL CIRCUIT Filed Oct. 6, 1947 p h p 3nventor (lttorneg Patented July 20, 1948 CONTROL CIRCUIT Hubert H. Wittenberg, Lancaster,-Pa., assignor.

to Radio Corporation of of Delaware America, a corporation Application October 6, 1947, Serial No. 778,217

My invention relates to electric discharge apparatus and more particularly to control or excitation circuits utilizing electric discharge means.

In some industrial applications, as for example in electric resistance spot weldin systems, it is desirable to employ control circuits which accurately determine the time interval of current flow.

It is an object of my invention to provide an improved control system supplying a current pulse of predetermined duration to a load.

A further object of my invention is to provide a control system whereby the current pulse interval can be accurately controlled.

An ancillary object of my invention is to provide a control means, simple in design, wherein the occurrence of such a current pulse is controllable by means of a switch or pushbutton device.

According to my invention, I provide a control system of simple structure for the main discharge apparatus through which current is supplied intermittently to a load. The system incorporates a gaseous discharge device normally maintained inoperative, an auxiliary electric discharge device, a circuit to provide an energizing pulse in predetermined phase relation to the anode potential of' the main discharge device, and a capacitor which is charged by the current pulse of the current through the auxiliary discharge device. The current pulse is conducted through the control electrode of the main discharge device causing conduction thereof. Charging of the capacitor prevents but a Single pulse through the main discharge device.

The organization and methodof operation, together with additional objects and advantages thereof will be apparent from the following description when read in connection with the accompanying drawing, in which the single figure shows schematically a specific embodiment of my invention.

Referring to the drawing, the apparatus shown comprises a welding transformer across the secondary of which a pair of welding electrodes 2 are connected. The electrodes engage the material to be welded and when the transformer I is energized, welding current. flows through the electrodes and the material. The primarywinding 3 of thetransformer I is supplied with power from the line conductors 4 and 5 in seriesw'lth the main discharge device 6 which is preferably of the immersed-ignition electrode type. The main discharge device comprises an anode 1, a mercury pool cathode 8, and an ignition electrode 9, immersed in the mercury pool. Arc discharges are initiated between the anode and cathode 8 by transmitting to the control member 9 a current of sufficient magnitude to initiate a cathode spot. In the chosen embodiment, this ignition current is supplied through an auxiliary discharge device ID of the gaseous discharge type, having an anode 9 Claims. (01. 315-252) a control electrode l2, and a heater type cathode l4. Heater voltage for its cathode is supplied by a transformer |5, the primary l6 of which is connected across the line conductors 4 and H in series with a resistor l8. The auxiliary discharge device, in combination'with an inductance l9, a

capacitor 20, the ignitor electrode 9, and the cathode 8, of the main discharge device, are in series with the line conductors 5 and I1.

current, thus prolonging the life of the auxiliary discharge device.

In parallel with the capacitor 20 is a series network comprising. a resistor 2| and contact points 23 and 24 ofa push-button switch 22. The control electrode l2 of the auxiliary discharge device is connected to its cathode |4 through acapacitor 25 which is adapted to stabilize the auxiliary discharge device against line surges and extraneous pickup. The control electrode I2 is also connected through a grid leak resistor 26 in parallel with a capacitor 2'i to a contact point 28 of the switch 22. Bias voltage for the auxiliary discharge device is composed of the heater voltage out of phase from the anode voltage, and a direct current component generated in the combination of the resistor 2'! and the condenser 28. The contact point ZBisreturned to the cathode l4 and one side of the secondary winding 29 of transformer I5 through a resistor 30. The side of the latter resistor, which is connected to the secondary winding 29 is also connected to the anode of a discharge device 3| as well as to one side of a load resistor 32 and a resistor 33. The other side of the resistor 33 is connected to a contact 3! of the switch 22. Discharge device 3| comprises an anode 34, a control electrode 49, and a hot cathode 36. The other side of the load resistor 32 is connected to the contact 31 of the switch 22 through acapacitor 38. This capacitor along with the resistor 33 forms a voltage divider network across the load resistor 32. There is also provided a transformer 39 having a primary winding 49,,a secondary winding 4|, and a terti-- ary winding 42; Primary potential is supplied by the voltage drop across the resistor IS. The tertiary winding 42 serves to provide heater voltage for the cathode 3B of the discharge device 3|. A phase shifting circuit, composed of a variable resistor 43 and a fixed capacitor 44, connected in series, is connected across the secondary winding 4|. The anode 34 of discharge device 3| is connected through the load resistor 32 to the common contact 45 of the capacitor 44 and the resistor 43 which is the source of potential for said anode. The cathode 35 of the discharge device 3| is connected to the center tap 45 of the trans- 3| and its associated circuit.

The inductance I9 is utilizedtoreduce the rate of rise of Between the points 45 and 4B is connected phase shift networkncomposedaof a resistor,

and a capacitor 48il The potential developed'iz across the capacitor 48 is used to supply excitation voltage to the control electrode 49 of the dis-, charge device 3|.

The theory of the operation of my devicezmayy best be understood by considering the well known fact that in a circuit containing resistancewand i capacitance the phase of the potential developed 10 across the capacitance will lag the phase potential developed across the resistance: bwapproxie:

mately ninety degrees. The instantaneousrrela-l tive magnitude of the potentials is dependent up on the relative value of impedance of the comwhich is* constant in magnitude but: variable in phase (by meansof the variable resistor 43) over It'is to be understood "that the capacitor 44 can be made'adjustable, and tliat'such an adjustment-would enable a greater phase shift;

llt will be seen that the total= potential difference of secondary win-ding 4i is'applied "across this? resistance 1 capacity series combination,

whereas the sourceofpotential for the anode 34 of the discharge device -3lis the common connection' of the resistor- 43and the capacitor 44.

Therelative magnitude of these potentials may be varied by adjusting -the relative values-of said capacitor and resistor, which are variable. Due to the quadrature phase relation of the potential difference across the capacitor-and the potential difference-across the resistortheresultant potentialdiffe'renc'e =between points 45 and 46 is adjustable in phase "relation withthe-potential across secondary'winding 4|. It will be clear that this is also a phase adjustment with'-re spectto the supply potential,

Again, it is known that in-order to efiectconduction of a gaseous discharge device, it is necessary to apply a positive potential to the control-"electrode circuit of -'the electric discharge devicaduringthe interval in whichsthe' anode potential" of -the electric dischargedevice is-'pos-= itive;= this phase :relation of "applied electroda potential will be referred to-as a favorable phase relation.

lt 'willbe seen that when the common connection' of the resistor and capacitor is positive-with" respect to the center tapla positive potential wii-l'loe applied throughthe 'anode load circuit of the discharge device 3| to the anode S t-and, at the same time, a sin'usoidal' voltage laggingthe anode voltage by 90",wil1 be developed across the capacitor. 48. This voltage is applied'to the control electrode 49 of the discharge device" 3|, ren-- de'ring it conductive. Conduction ofx'the discharge device persists for the remainder of the cycle;- or 90: Rapid ionization of the discharge deVice'S-Lwhich is of the gaseous type, causesa pulse similar to that obtained from--a peaking transfo'rmerthus causing a steep positive wave front" to be developed across the anode load resister-'32. The capacitor 38' and the resistor -33 difierentiatethe voltage across the resistor 32 so that a pulse-appears across the resistor 33. This excitation pulse occurs-atthe same-frequency as" that of the supply potential:

When a 'welding pulse is desired switch '22 is depressed causing electrical contact between switch contact points 3'land 28' andfihnce; the

application of a pulse of positive potential to the .control. electrode l2.lof,-the -auxiliary discharge device it. This pulse is of sufficient magnitude to overcome the bias which is normally negative, on the control electrode, and is adjustdevice, causing said device to be rendered conductive in view of the fact that said current is in favorable phase relation to impressedpotential of the main discharge device; I

The main discharge device 6 will remain con ductive during the remaining portionof'the half cycle ofanode cathode voltage; but by reason 10!?" the alternating nature of the supply potential conduction by the main discharge device will ceasewhen the potential falls below'that re- .quired to maintain ionization. The pulse of cure rent through the main'discharge device is drawn through the primary '3 of. welding transformer l and by transformer action a potentialand con sequently a welding current is. produced in "the secondary Winding 2. .Only a single. pulse occurs because the ignition pulse through auxiliary dise charge devicelfl chargescondenser 20"to line. potential preventing furtherv current flow until switch 22 is released causingv electrical tcontactr between contact points and 23. and allowing, condenser 23. to discharge throughiresistorjlh The charging time of said condenseris.smalLwith; respect to the period of the supply potential.

It is ,to be understood thatthe form of my in-... vention, herewith shown and described is toibe'. taken asa preferred example of the same; and if thatvarious changes in theshape, sizehandrarrangementof parts may be resorted to, without departing from the spirit ofmy invention,- 4 or.-. thescope of the subjoined claims.

Having-thus described my invention, I claimz 1. In, a control systemya source "of alternate. ing potential, a load, a main discharge device; connected in series :with saiddoadacross-:the sourceof-"potential; said main discharge, device having an aignitor: electrode" and a mercury .pool cathode, an auxiliary discharge device having an anode; a cathode, and a control electrode-,-a.-circuitconnecting the cathode of said auxiliary dis-i=- charge device to said ignitor electrode, an'elec-v tric; storage device interposed' between said :anode and-said source of potential, circuit connected-so as: to provide-a potential pulse in predetermined time relatiorr to said supply potential; andwa cir-" cuit" applying said pulse to saidzcontrolelectrodez'z 23 Inacontrol system; a source of alternate ing::potential-,=- a :load; said loadc0mprising.--:a:- transformer having a primary winding and'ra z secondary winding, a main discharge device cone. nected in series-with said primary winding: across said sourceof potential,saidmain dis charge device having anignitor electrodeandc'a: mercury pool cathode, an auxiliary discharge deH vice having an anode, a cathode,*and a control" electrode, a circuit connecting the cathode of" said auxiliary discharge device to said-ignitorelectrode, an electric storage device interp'osed between said anode and said source of potential,-'.- a'puls'e circuit connected soas to provideapotential pulse 1 in predetermined time relation "to c said supply potential, and a circuit applying said pulse to said control electrode.

3. In a control system, a source of alternating potential, a load, said load comprising a transformer having a primary winding and a secondary winding, a main discharge device connected in series with said primary winding across said source of potential, said main discharge device having an ignitor electrode and a mercury pool cathode, an auxiliary discharge device having an anode, a cathode and a control electrode, a circuit connecting the cathode of said auxiliary discharge device to said ignitor electrode, an electric storage device interposed between said anode and said source of potential, a pulse circuit connected so as to provide a potential pulse in predetermined time relation to said supply potential, means for adjusting said time relation, and a circuit applying said pulse to said control electrode.

4. In a control system, a source of three phase alternating potential, a load, a main discharge device connected in series with said load across one of said phases, said main discharge device having an ignitor electrode and a mercury pool cathode, an auxiliary discharge device having an anode, a cathode and a control electrode, a circuit connecting the cathode of said auxiliary discharge device to said ignitor electrode, an electric storage device interposed between said anode and another of said phases, a pulse circuit connected so as .to provide a potential pulse in predetermined time relation to said three phase potential, and a circuit applying said pulse to said control electrode.

5. In a control system, a source of three phase alternating potential, a load, said load comprising a transformer having a primary winding and a secondary winding, a main discharge device connected in series with the primary winding of said load across one of said .ph'ases,-said main discharge device having an ignitor electrode and a mercury pool cathode, an auxiliary discharge device having an anode, a cathode and a control electrode, a circuit connecting the cathode of said auxiliary discharge device tosaid ignitor electrode, an electric storage device interposed between said anode and another of said phases, a pulse circuit connected soas to provide a potential pulse in predetermined time relation to said three phase potential, and a circuit for applying said pulse to said control electrode.

6. In a control system, a source of three phase alternating potential, a load, said load comprising a transformer having a primary winding and a secondary winding, a main discharge device connected in series with the primary load winding of said load across one of said phases, said main discharge device having an ignitor electrode and a mercury pool cathode, an auxiliary discharge device having an anode, a cathode, and a control electrode, a circuit connecting said cathode to said ignitor electrode, an electric storage device interposed between said anode and another of said phases, a pulse circuit connected so as to provide a potential pulse in predetermined time relation to said three phase potential, means for adjusting said time relation, and a circuit applying said pulse to said control electrode.

'7. In a control system, a source or three phase alternating potential, a load, said load comprising a transformer having a primary Winding and a secondary winding, a main discharge device connected in series with the primary load winding of said load across one of said phases, said main discharge device having an ignitor electrode and a mercury pool cathode, an auxiliary discharge device having an anode, a cathode and a control electrode, a circuit connecting the oathode of said auxiliary discharge device to said ignitor electrode, an electric storage device interposed between said anode and another of said phases, bias means applied to said auxiliary discharge device, said bias being 180 degrees out of phase with said anode potential, a pulse circuit connected so as to provide a potential pulse in predetermined time relation to said supply potential, and a circuit applying said pulse to said con-- trol electrode so as to overcome said bias.

secondary winding, a main discharge device con-- nected in series with the primary load winding of? said load across one of said phases, said main.

discharge device having an ignitor electrode and a mercury pool cathode, an auxiliary dischargedevice having an anode, a cathode and a control. electrode, a circuit connecting the cathode of? said auxiliary discharge device to said ignitor electrode, an electric storage device interposed. between said anode and another of said' phases,. bias means applied to the auxiliary discharge device, said bias being degrees out of phase with: said anode potential, a pulse circuit connected so as to provide a potential pulse in predetermined time relation to said three phase potential, means for adjusting said time relation, and a circuit applying said pulse to said control electrode so as to overcome said bias.

9. In a control system, a source of three phase alternating potential, a load, said load comprising a transformer having a primary winding and a secondary winding, a main discharge device connected in series with the primary load winding of said load across one of said phases, said main discharge device having an ignitor electrode and a mercury pool cathode, an auxiliary discharge device having an anode, a cathode and a control electrode, a circuit connecting the oathode of said auxiliary discharge device to said ignitor electrode, an electric storage device interposed between said anode and another of said phases, bias means applied to said auxiliary discharge device, said lbias being 180 degrees out of phase with said anode potential, a pulse circuit connected so as to provide a potential pulse in predetermined time relation to said three phase potential, means for adjusting said time relation, and a circuit including a switch applying said pulse to said control electrode to overcome said bias.

HUBERT H. WITTENBERG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,231,674 Ludwig Feb. 11, 1941 2,320,916 Dawson June 1, 1943 

